|
 Convex Hull? |
| Posted by Jason Campbell on Jan-13-2016 01:35 |
|
Peter,
I have seen mention of the use of convex hull calculation for ChartDirector's 3D surface
plots. I wanted to ask before committing to testing in code, will ChartDirector handle a
complete 3D cloud of points and skin it properly (convex hull) around the entire volume of
points? Imagine points along the surface of a sphere... Or will it only do so for the top layer
of points (as if to lay a blanket on top of all the points and only render a flat surface)? I
have seen no examples in the gallery of what I am looking to do so I wanted to ask. Thank
you! |
| Re: Convex Hull? |
| Posted by Peter Kwan on Jan-13-2016 14:35 |
|
Hi Jason,
In ChartDirector, the surface chart is the same as a contour chart or heat map, except that
the visualization is in 3D. The "convex hull" refers to the boundary of the surface, which is
a polygon. It is computed using the x and y coordinates only.
If you give ChartDirector a random set of points on the top-half of the sphere surface, it
will plot the top-half of a sphere surface. See:
http://www.advsofteng.com/doc/cdcpp.htm#surfacewireframe.htm
If the random points are on both halves of the sphere surface, ChartDirector will still plot
them as usual. If you will look at the points from the top, the points will lie within a circle
(the convex hull). If the mid-point of the sphere is the z = 0 plain, there will be random
points with positive and negative z coordinates. If you imagine it is a heat map, it just like
some randomly distributed hot and cold spots. ChartDirector will plot the surface as usual,
which probably would look like a surface with random sharp peaks and deep valleys. It
may not be what you expect.
So in summary, the "convex hull" refers to the boundary of the surface, which is a
polygon. The surface itself is not a convex hull. (If the convex hull is a surface, then the
data points should represent a "solid", not a surface. but ChartDirector currently does not
have "solid" charts.)
Regards
Peter Kwan |
| Re: Convex Hull? |
| Posted by Jason Campbell on Jan-16-2016 22:49 |
|
Peter,
Are there any plans to add functionality to wrap the entire surface of a cloud of points?
Something along the lines of the attached image...
PS> Understood about your point regarding convex hull. My question was more this, in after
the convex hull calculation identifies the outermost points, is be able to skin them all the way
around, not just a top-most surface as you presented in your reply.
Thanks!
|
| Re: Convex Hull? |
| Posted by Peter Kwan on Jan-19-2016 02:15 |
|
Hi Jason,
Unlikely, the convex hull for a solid (a surface that bounds the solid) is significantly
different from the convex hull for a surface (a polygon which bounds the surface).
ChartDirector currently cannot compute convex hull for a solid.
Regards
Peter Kwan |
|
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